Does the muscle cramp up or are you in too much pain to run. Seems like the cross-training is going well, so focus on that. Any chance you can see a physical therapist? I know it's tough to get an appointment in Sweden, but it seems like it may be necessary at this point.
Are you doing a little hamstring and butt strength, as well as resting and stretching and icing? Seems like that might help, especially in the long term.
I have an appointment for Thursday, as that was the earliest they said they could fit me in. I am stretching and rolling and massaging (sometimes with ibuprofen cream). I'm going strength for the hamstring and butt as well (exercises that I found online). It starts to cramp up and the pain spreads up and down my hamstring as I run and feels like it's going to pull apart. Which normally I would maybe just run through, but after hurting it I feel very cautious.